Minerals, vitamin D, and parathyroid hormone in continuous ambulatory peritoneal dialysis

Abstract

The effects of continuous ambulatory peritoneal dialysis on parathyroid hormone (PTH) and mineral metabolism were evaluated in ten patients. Utilizing a PTH radioimmunoassay, which measures both intact hormone and carboxyl-terminal PTH fragments, it was found that the mean clearance of immunoreactive parathyroid hormone was 1.5 +/- 0.73 ml/min (SEM) yielding a daily net removal of 13.6 +/- 3.2% of estimated total extracellular parathyroid hormone. Gel electrophoresis of the dialysate revealed the presence of both intact parathyroid hormone and fragments in a similar pattern to that of peripheral plasma. Normal levels of 25-(OH) vitamin D and vitamin D binding protein were observed prior to the initiation of continuous ambulatory peritoneal dialysis and following 6 months of treatment. Timed dialysate collections (N = 93) demonstrated a daily calcium influx of only 9.9 +/- 9.7 mg. The daily removal of phosphorus was 308.4 +/- 15.5 mg. Despite elevated serum magnesium levels in all patients, the net daily removal was inadequate (31.2 +/- 15.5 mg). It was concluded that: (1) Unlike chronic hemodialysis, continuous ambulatory peritoneal dialysis removes significant amounts of parathyroid hormone. (2) Normal 25-(OH) vitamin D and vitamin D binding protein levels are maintained with continuous ambulatory peritoneal dialysis despite large protein losses. (3) Substantial amounts of phosphorus are removed with continuous ambulatory peritoneal dialysis but not to an extent that precludes use of phosphorus binders. (4) Dialysate containing lower magnesium and possibly higher calcium concentrations should be made available to improve mineral homeostasis.

Clearance of Osteocalcin by Peritoneal Dialysis in Children with End-Stage Renal Disease

“…It is likely that the high clearance rate is due to the transfer of substantial amounts of smaller immunoreactive osteocalcin fragments. Immunoreactive PTH has also been identified in the serum and dialysate of CAPD patients (22). As with osteocalcin, its peritoneal clearance is high relative to other proteins.…”

Control of Hyperphosphatemia among Patients with ESRD

“…This seems to be due to the high postdialysis rebound from mobilization of phosphate from the intracellular space and/or bone induced by intradialytic removal of this solute. Moreover, the clearance of phosphorus during peritoneal dialysis is comparable or inferior to that of conventional hemodialysis, especially when intradialytic protein loss is taken into consideration (20). Hence, the need for phosphate binders for the majority of patients with ESRD is predictable.…”

Causes and Consequences of Adynamic Bone Disease

“…(4)  Loss of PTH: Significant amounts of PTH [71, 72]and osteocalcin [72]are lost into the peritoneal fluid, amounting to a clearance of 2 ml/min, and a loss of 14% of extracellular PTH. The clinical significance of this loss is uncertain, but could contribute to the increased ABD incidence seen in CAPD.…”